What is the error “Every derived table must have its own alias” in MySQL?

Question

I am running this query on MySQL

SELECT ID FROM (
    SELECT ID, msisdn
    FROM (
        SELECT * FROM TT2
    )
);

and it is giving this

Answer 1

I arrived here because I thought I should check in SO if there are adequate answers, after a syntax error that gave me this error, or if I could possibly post an answer myself.

OK, the answers here explain what this error is, so not much more to say, but nevertheless I will give my 2 cents using my words:

This error is caused by the fact that you basically generate a new table with your subquery for the FROM command.

That's what a derived table is, and as such, it needs to have an alias (actually a name reference to it).

So given the following hypothetical query:

SELECT id, key1
FROM (
    SELECT t1.ID id, t2.key1 key1, t2.key2 key2, t2.key3 key3
    FROM table1 t1 
    LEFT JOIN table2 t2 ON t1.id = t2.id
    WHERE t2.key3 = 'some-value'
) AS tt

So, at the end, the whole subquery inside the FROM command will produce the table that is aliased as tt and it will have the following columns id, key1, key2, key3.

So, then with the initial SELECT from that table we finally select the id and key1 from the tt.